Frosty Tech says the Sunbeam, however it more depends on the fan you use on the heatsink. I don't think they use the same fan on all the heatsinks they test. However using the fan that comes with it, the Sunbeam apparently is a bit cooler though also noisier.

I second the S-Flex. They are about even with the Noctua P12's, but when some restriction is put on the airflow (radiator, heatsink, etc) the S-Flex pulls ahead. But, if you don't mind some noise, there are many extremely powerful 38mm thick fans that will provide lots of airflow and pressure, but they are loud. If you can find it, the San Ace H1101 is probably the best fan out of all high speed fans (high speed bing 100-130CFM), but it is nearly impossible to find and costs around $20-25.